Age-associated changes in cartilage matrix alter its ability to provide pain-free joint movement. Changes in matrix proteoglycans affect cartilage biomechanics, making aged tissue more susceptible to damage. Indeed, age is the major risk factor for osteoarthritis (OA), a chronic degenerative condition that affects ~20 million people in the US. This project tests the hypothesis that Wnt family proteins regulate cartilage matrix synthesis, and that this function is altered in old age and in OA. This hypothesis is synthesized from two well-established lines of evidence: 1) Cartilage matrix glycosaminoglycan (GAG) content, structure, and sulfation change with age and OA, and 2) The amount and sulfation of matrix GAGs influence Wnt signaling and expression. Additional evidence to support our hypotheses is that nuclear b-catenin, an indicator of Wnt signaling, is found in adult cartilage, and our Preliminary Studies show expression of many Wnt ligands, receptors, signaling and target genes in adult chondrocytes. Wnt proteins have also been shown to regulate matrix synthesis by chondrogenic cells in vitro. The proposed studies will use human articular chondrocytes isolated from discarded tissues of patients undergoing total knee replacement. Specific Aim l is to define the Wnt component expression profile of adult chondrocytes (30-50 years), and compare it to aged (>70 years) and OA chondrocytes. Specific Aim II is to investigate the link between Wnt signaling and chondrogenesis, and determine whether this is decreased in aged and OA chondrocytes. Our results will have a significant impact on understanding mechanisms of normal and pathologic aging of cartilage, and may lead to novel therapeutic and preventative strategies to rejuvenate cartilage. This work will also provide a solid foundation for future research on Wnts in cartilage biology.